The present invention relates to improvements in the technology for observing the surface shape of a sample by utilizing a tunnel current or a field emission current that generates when the probe tip is brought close to the surface of a sample and when a voltage is applied across them. More specifically, the invention relates to a scanning tunneling microscope which is so improved as to be adapted to obtaining topographic information on the surface of the sample within short periods of time by scanning a wide scanning field on the surface of the sample at high speeds using the probe tip or to obtaining topographic information on the surface of the sample which consists of a high resistance material, and further relates to a new surface topographic observation method.
A scanning tunneling microscope according to the prior art has been discussed in, for example, Physical Review Letters, 49, 1982, pp. 57-61.
According to the scanning tunneling microscope of the above prior art, attention has not been given to measuring the surface shapes when the scanning field (surface region to be observed) is wide on the surface of the sample or when the electric resistance is very great on the surface of the sample. In the former case, i.e., when a wide scanning field is to be measured, a very extended period of time is consumed for the scanning and in the latter case, i.e., when the surface having a high resistance is to be measured, the electronic current does not flow steadily making it difficult to take measurement maintaining reliability. In the former case, in particular, atoms react with each other between the probe tip and the surface of the sample. Therefore, atomic size resolution is required for the scan control system of the scanning tunneling microscope. In the prior art, however, since the scanning control system exhibits low response characteristics, the scanning time must be increased with the increase in the scanning field. When a square surface to be observed having a side of about 2.5 .mu.m is scanning with a raster scan line number of 256 according to the prior art, the scanning time (for measurement) of about 90 minutes is required. When a wider surface is to be observed, furthermore, the scan lines are lengthened and the time required for measurement increases in proportion to the length of the scan lines.